1. Field of the Invention
The present invention relates generally to digital image processing and editing, and more specifically, to methods for automatic detection and removal of red eye effect in digital images.
2. Description of the Related Art
Taking photographs of people and using flash often results in an artifact in the photograph commonly known as “red eye.” The artifact can be present in an image taken from either a traditional film camera with flash, or a digital camera with flash. The artifact is generally manifested as an apparent red coloration of the iris of the eye, instead of the natural eye coloration, and is also referred to as “flash effect.”
Red eye is generally caused by the reflection of the intense light of a flash from the blood vessels of the retinas of a person's eyes. The degree of dilation of a subject's eyes varies the apparent size of the red eye area. Because increased eye dilation results in a corresponding increase in red eye, it is common for attempts to reduce red eye to include measures to decrease eye dilation such as increasing ambient lighting, having a subject stare into a bright light just prior to taking a picture using flash, and so forth.
FIG. 1A is a diagram of an eye 10 illustrating a typical red eye effect as it might appear in a photographic image. Outer iris area 12 may or may not be rendered with apparently normal coloration (e.g., blue, green, brown, etc.). Pupil area 14 typically exhibits the redness that is known as red eye, and a small region 16 within pupil area 14 typically includes a bright white flash reflection.
Whether a photograph is taken with a traditional film camera or with a digital camera, the photograph can be, and often is, rendered as a digital image that is capable of being edited, cropped, re-touched, or otherwise modified. Popular digital photo editing applications include tools for image editing that include the ability to modify or correct red eye effect in image subjects. Such tools are generally manually manipulated to the effected area, and then may be implemented in a manual or semi-automatic mode to correct red eye. FIG. 1B shows the eye 10 image of FIG. 1A with a typical digital image editing tool set of a computer program such as a photo editing application of a computer system implemented for red eye correction. Eye 10 image includes outer iris area 12, pupil area 14, and small region 16 within pupil area 14 having bright white flash reflection. A selection box 18 may be defined around the general area of the red eye effect to be corrected. A user or operator usually defines the selection box 18 around the area desired to be corrected. In other words, a computer user or operator must identify an area or region in a digital image, which is stored as electrical signals in a computer system and displayed on a computer display output, and in some manner effect a selection or identification of the area for correction.
In some applications, a simple selection box 18 is sufficient to identify the area. If the photo editing application includes some measure of semi-automatic correction, the defining of the selection box 18 may be all that is required of the user or operator prior to indicating an acceptance or rejection of the semi-automatic red eye correction within the selected or identified area. In some applications, a computer user or operator must scale the digital image to achieve as large an image as possible, or desired, and then must correct the color within the pupil region 14 of the eye 10 one pixel at a time until the desired color correction is effected. Typically, a pointer 20, which may be in the shape of an arrow as illustrated, or in the shape of a paintbrush, a fountain pen, a sprayer, and so forth depending on the specific editing application, is used to select each pixel within the effected area, one at a time, and then each selected pixel is changed to a desired color. In semi-automatic applications, the pointer 20 is typically used to define, size, and position the selection box 18 over the area to be corrected.
In both the manual and the semi-automatic editing applications, some deliberate act of a user or operator is required to either identify, or to identify and to correct, the red eye effect. The process can be tedious, time-consuming, and require patience and manual dexterity. What is needed is a method for automatic detection and correction of red eye effect in digital images, effective in digital images rendered from a digital imaging device or from a traditional camera and film.